An energy-absorbing foam is a specially designed foam that reduces the load a passenger of a vehicle experiences, thereby reducing potential injury. There has been a long-felt need in the automotive industry to develop a method for making an energy-absorbing foam with recycled polyurethane fillers that has properties that are comparable to a foam made without fillers. Ideally, such a method would reduce the amount of automotive shredder residue which ends up in landfills after automobiles are scrapped. Reusing or recycling polyurethane foams would also reduce the need for fresh reactants resulting in conservation of our petroleum reserves. Also, such a method would reduce the amount of polyurethane waste that is currently disposed of--a substantial amount. Each year, for instance, more than 10 million automobiles containing an appreciable amount of polyurethane outlive their usefulness and are scrapped. Of those automobiles scrapped from 1980 to 1994, there was an average of about 90 kg (200 lbs.) of plastic per vehicle. Of that, roughly 25% was polyurethane.
There are two methods for recycling polyurethane foams. In one method involving glycolysis, the foam is ground and the polyurethane is transesterified by heating in a low molecular weight glycol such as ethylene or diethylene glycol to give a mixture of urethane-containing polyols and free glycol. The mixture is then used as a chain extender in a fresh polyol blend. The method is disadvantageous because it is an energy intensive chemical process and because small amounts of aromatic diamines can be formed as a by-product of glycolysis.
In another method, polyurethane regrind is used as a filler by suspension in a fresh polyol blend. In this process, small pieces of foam (4 to 8 in. cubes) are first reduced to particles less than 0.5 in. using a common granulator or rotary knife cutter. The particles are then reduced to a powder using one of a number of techniques which use shear, impact or compressive forces, to pulverize the foam (such as those using fitzmills, hammermills, air-swept pulverizers, and two-roll mills). The powder is typically collected with a centrifugal cyclone filtering system after which it is packaged and readied for introduction into the polyol as filler. Measured amounts of polyurethane powder are added via a feed screw to a predetermined quantity of polyol in a blend tank. A uniform mixture can be created by thorough agitation with a high-speed mixer capable of handling high viscosity liquids. Particles should be smaller (&lt;200 microns) than the original cell size because intact cells will swell with polyol blend, rendering the system with an unprocessable viscosity. The use of fillers in such foam-making methods have produced foams with undesired energy-absorbing properties, and as such, the methods have not been used with any appreciable degree of commercial success.
U.S. Pat. No. 5,847,014 is directed to an isocyanate-reactive mixture containing at least one non-filled polyether polyol, at least one non-tertiary amine containing polyether polyols, and water. The patent is also directed to a water-blown energy absorbing foam produced by reacting this mixture with (i) a polymethylene poly(phenyl isocyanate), a silicone cell-opening surfactant, catalysts, and at least one tertiary amine catalyst. The patent does not discuss the making of polyurethane foams with polyurethane fillers.
Nodelman et al, "A Viable Technology for the Recycling of Polyurethane Energy-Absorbing (EA) Foams" presented at The Society of Automotive Engineers (February 1997), discloses that the compressive strength of a semi-rigid polyurethane foam made with polyurethane fillers can be influenced by the surfactant used to stabilize the cellular structure before gellation. The paper also shows that addition of a solid filler to polyurethane foam reduces the impact strength during dynamic impact testing if a specific surfactant is used. The reference discloses an energy-absorbing foam made with polyurethane fillers which allegedly has properties that are comparable to a foam made without fillers. The paper, however, does not describe the surfactant that is used. In view of the fact that there are literally millions of different types of surfactants that can be used to make energy-absorbing foams, the reference does not enable the invention.
In Dimitroff, "New Surfactants and Catalysts Developed for Energy-Absorbing Polyurethane Foam", Polyurethanes Expo, 1996, the authors discuss surfactants which are said to form foam having a high open-cell content with good cell stabilization. The paper discusses systems which involve rigid, friable isocyanurate foams and does not discuss systems involving semi-rigid foams. The paper does not discuss systems in which foams are made with fillers.
It would be desired to develop a method for making a recycled foam that overcomes the disadvantages discussed above.